1. Field of the Invention
The present invention relates to a relatively displacing apparatus, such as a turbocharger, a gas turbine and the like, which comprises a movable member and a stationary member disposed adjacent to each other and displacing relatively at a high temperature. In particular, the present invention relates to a relatively displacing apparatus which enables to make a clearance between the movable member and the stationary member zero (0) substantially during the operation thereof.
2. Description of the Prior Art
A conventional relatively displacing apparatus will be hereinafter described with reference to an automotive turbocharger illustrated in FIG. 24. This turbocharger has a turborotor 100 and an impeller 200 as a movable member, and a turbohousing 101 and a compressor housing 201 as a stationary member. In the operation of the turbocharger, the turborotor 100 is rotated by the energy of the exhaust gas of an engine (not shown), a shaft 300 is then rotated, and the impeller 200 is rotated by the rotation of the shaft 300, whereby air is supercharged into the engine. In this way, the turborotor 100 and the turbohousing 101 as well as the impeller 200 and the compressor housing 201 are disposed adjacent to each other and displaced relatively at a high temperature during the operation of the turbocharger.
Here, it has been known that the efficiency of the turbocharger can be improved by making a clearance C100 between the turborotor 100 and the turbohousing 101 and a clearance C200 between the impeller 200 and the compressor housing 201 as small as possible. In the case that the clearances C100 and C200 are reduced, however, there is a possibility of damaging the turborotor 100 and the impeller 200 since the eccentricity and so on occurred during the manufacture of the shaft 300 results in the contact or collision of the turborotor 100 with the turbohousing 101 and the contact or collision of the impeller 200 with the compressor housing 201.
Accordingly, in the conventional turbocharger, it is necessary to set the clearance C100 between the turborotor 100 and the turbohousing 101 at approximately 0.6 to 0.8 mm and to set the clearance C200 between the impeller 200 and the compressor 201 at approximately 0.3 to 0.5 mm. The conventional turbocharger thus has insufficient efficiency. Therefore, it has been desired to develop a technology which can improve the efficiency of the conventional relatively displacing apparatus by making the clearance between the movable member and the stationary member as small as possible and which can avoid the damage to movable member.
A technology has been disclosed so far in which a coating layer composed of a mixture of soft metal and resin or graphite is formed on the compressor housing 201 by flame spray coating. In the conventional technology, the formed coating layer is easily machined off by the contact of the impeller 200 with the compressor housing 201 resulting from the eccentricity and so on of the shaft 300. Whereby it is possible to make the clearance C200 between the impeller 200 and the machined compressor housing 201 zero (0) substantially. Here, the impeller 200 is not damaged by the operation. The technologies disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 18085/1974 and U.S. Pat. No. 4,405,284 are included in the category of the technology which utilizes the machinability of the coating layer in order to make the clearance between a movable member and the stationary member zero (0) substantially. These publications disclose technologies of an Ni-graphite coating and an NiCrFeAl-BN coating.
Further, U.S. Pat. No. 4,269,903 discloses an invention relating to a ceramic seal. The publication discloses a technology for coating a porous stabilized zirconium oxide layer having a porosity of 20 to 33%. This technology is basically identical with the above-mentioned technology. According to this technology, it is also possible to make the clearance between the movable member and the stationary member zero (0) substantially by utilizing the machinability of the porous stabilized zirconium oxide layer.
However, even when the relatively displacing apparatus is manufactured by the above-mentioned technologies, there arises the following problems in the relatively displacing apparatus manufactured.
Namely, the technology disclosed in the U.S. Pat. No. 4,269,903 utilizes the zirconium oxide, which is resistant to thermal shock, as the coating layer in view of the high temperature application. The zirconium oxide is made porous in order to secure the machinability of the coating layer. However, since the coating layer having the porosity of 20 to 33% is formed by flame spray coating the zirconium oxide only and since the zirconium oxide having a high hardness of Hv 1000 or more is contained therein according to the technology, the movable member, i.e., a mating member of the coating layer, is likely to be worn by the coating layer. Further, when a coating layer having a porosity of 33% or more, for instance a coating layer having a porosity of 40% is formed in order to improve the machinability, the thermal shock resistance of the coating layer deteriorates and the coating layer comes off or falls off accordingly.
Further, since the coating layer is metallic in the technologies disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 18085/1974 and the U.S. Pat. No. 4,405,284, it is impossible to endure a severe application condition, for instance the application condition of an aircraft engine or a gas turbine engine, i.e., a high temperature of approximately 1000.degree. C. at maximum for a long period of time. The coating layer is eventually oxidized and corroded, and it should be repaired accordingly.
In addition to the above-mentioned technologies, Japanese Examined Patent Publication (KOKOKU) No. 690/1975 discloses an invention relating to a gas turbine engine. The publication does not disclose the technology utilizing the machinability of the coating layer, but discloses a technology for avoiding the damage to a turbine blade in which a turbine casing is molded and sintered with a soft ceramic material being softer than a material for forming the turbine blade. However, since the force for binding the ceramic materials is weak, the gas turbine engine manufactured by the technology lacks the durability.
Moreover, Japanese Unexamined Patent Publication No. 168926/1987 discloses a technology for optimizing the clearance between the turborotor 100 and the turbohousing 101 or the clearance between the impeller 200 and the compressor housing 201 in which the inner surface of the turbohousing 101 or the compressor housing 201 is coated with a composite material. However, the publication does not disclose the quality of the coating layer material at all.